Synopsis At 0645 Coordinated Universal Time (UTC), Air Transat Flight 961 (TSC961), an Airbus A310-308 aircraft, departed Varadero, Cuba, for Qubec, Quebec, with 9crew members and 262passengers on board. At approximately 0702UTC, the aircraft was 90nautical miles south of Miami, Florida, United States, and in level flight at flight level (FL)350, when the flight crew heard a loud bang and felt some vibration. The aircraft entered a Dutch roll and the captain disconnected the autopilot to manually fly the aircraft. The aircraft climbed nearly 1000feet while the captain tried to control the Dutch roll. The crew initiated a descent back to FL350 and requested further descent and a possible diversion to Fort Lauderdale, Florida. During the descent, the Dutch roll intensity lessened and then stopped when the aircraft descended through FL280. No emergency was declared. When the aircraft was abeam Miami, the crew decided to return to Varadero. During the landing flare, the rudder control inputs were not effective in correcting for a slight crab. The aircraft landed and taxied to the gate. After shutdown, it was discovered that the aircraft rudder was missing. Small pieces of the rudder were still attached to the vertical stabilizer. One flight attendant suffered a minor back injury during the event. Ce rapport est galement disponible en franais. Minister of Public Works and Government Services Canada 2007 Cat. No. TU3-5/05-2E ISBN 978-0-662-46783-0 How This Report Is Organized A05F0047 Air Transat Investigation Report Appendices Transportation Safety Board of Canada - AVIATION REPORTS - 2005 - A05F0047 Transportation Safety Board of Canada Common menu bar links Franais Home Contact Us Help Search canada.gc.ca REPORTS AVIATION 2005 A05F0047 Institutional links AVIATION REPORTS - 2005 - A05F0047 2.5.7.1 Summary of Important Points The dynamic event was most probably caused by rudder flutter. Flutter analysis showed that the rudder would only flutter under the occurrence conditions if it were damaged. Therefore, the rudder was most probably damaged. Flutter analysis determined that the amount of damage necessary to cause flutter was significant. The occurrence conditions had been experienced by the aircraft many times previous, but the rudder had not experienced vibration, flutter, or failure. Therefore, the original damage was most likely small and grew over time. Although the mechanical cycling tests that were conducted during the original certification showed no damage growth, vacuum cycling tests conducted during this investigation demonstrated that it is possible for an initial damage to grow due to pressure differential associated with altitude. Results of investigative activity did not support the likelihood of a blunt impact scenario. A discrete event could not be discounted as a possibility since most of the rudder was not recovered for examination. Positive indications were found suggesting the possibility of a weak z-section bond at the interior lower front of the left side panel, and analyses showed that such damage could grow under vacuum loads. The interior skin is not easily accessible for inspection, and at the time of the occurrence, there was no inspection program for the inner skin. If the damage had been growing on the interior, it would not have been found by the existing inspections. A weak z-section bond would manifest itself in the bond of the inner skin. In the time leading up to, and at the time of the occurrence, the aircraft was neither manoeuvring nor experiencing turbulence. Therefore, the most significant load on the rudder would have been pressure differential between the core interior and the ambient air at altitude. This suggests that differential pressure may have driven the event. The investigation revealed that the first event in the occurrence sequence was a loud bang. Vacuum cycling damage growth tests found that, when the damage reached critical size, it grew explosively with a sudden violent release of energy, which caused a loud noise. The vacuum cycling tests found that explosive damage growth was so violent that it damaged the interior of the test chamber. In flight, such a violent event could possibly damage the opposite side panel. The flight dynamics analysis found that there was a large lateral force at the rudder, possibly the explosive damage growth in one side panel striking the other side panel. The sudden explosive growth of damage in one side panel and possible collateral damage to the adjacent panel would have resulted in a sudden reduction of rudder stiffness. The flutter analysis indicated that such a loss in stiffness could lead to flutter under the occurrence conditions. The time-domain flutter analysis for the large disbond case found that, shortly after the initiation of flutter, a large aft force at hinge5 would exceed the failure load. This is consistent with the flight dynamics analysis that found that, shortly after the initial event, there was a large aft and downward tug on the tail. This is also consistent with the damage observed at hinge5. The time-domain flutter analysis for the large disbond case also found that the next hinge to fail would be hinge6, and that the loads on the rear VTP main attachment fittings would exceed ultimate strength. This is consistent with the damage observed at hinge6 and at the VTP attachments. 2.5.7.2 Most Likely Failure Scenario Some time before the occurrence flight, a disbond or in-plane core fracture occurred. The cause of this initial damage may have been a discrete event or a weak bond at the z-section. An indication of weak bonding was found at the z-section along the interior lower front of the left side panel. This damage then grew, possibly due to reduced pressure cycling loads associated with normal flight, without detection until it reached a critical size. During the occurrence flight, having reached the critical size, the damage rapidly propagated, resulting in a loud and sudden explosion of the skin. This separation could have damaged the opposite side panel and created a large sideways force on the empennage. The resulting sudden reduction in torsional stiffness led to the onset of rudder flutter. About one second later, there was a large aft and downward force associated with failure of the upper hinge points, as the rudder separated. The rudder-separation event lasted about seven seconds, after which only 16percent of rudder effectiveness remained. During the remainder of the flight, more rudder pieces separated, and the aircraft landed with no aerodynamically effective rudder remaining. Main Links TSB Home Proactive Disclosure Marine Pipeline Rail Air Air Investigation Reports Recommendations and Assessments of Responses Board Concerns Air Statistics Reporting an Air Occurrence Air Investigation Reports Recommendations and Assessments of Responses Board Concerns Air Statistics Reporting an Air Occurrence